The present invention generally relates to pneumatic tires, specifically tires with modified sidewall ply lines and bead sections to increase the load carrying capacity.
The sidewalls of conventional pneumatic tires provide these conventional tires with desirable flexibility in the radial direction. This radial flexibility allows the tread surface to move radially inward to accommodate irregularities in the road surface. However, the sidewalls of conventional tires also limit the performance of the tire with undesirable axial and circumferential flexibility. Axial sidewall flexibility limits the responsiveness of the tire in cornering, and circumferential flexibility limits the tire""s capacity to handle the torsional forces encountered in acceleration and deceleration. In addition, the space required for the sidewall limits the maximum size of the wheel and the size of the brake mechanism that can be fit within the wheel for a given overall tire diameter.
When normally inflated, the sidewalls of conventional tires protect the rim from possible contact with the road surface. Also, conventional sidewalls distribute the weight of the vehicle and the force of impacts with road hazards by acting in tension to confine the compressive force provided by the air in a normally inflated tire. However, when normal inflation air pressure is lost, such as when the tire is punctured, the relatively thin and flexible sidewalls of a conventional tire collapse and buckle in such a manner that the sidewall fails to provide its normal functions of radial flexibility, rim flange protection, or the distribution of forces from the wheel to the road.
The load carrying capacity (LCC), typically represented by the Load Index (LI), of a pneumatic tire is related to the tire fill pressure (P) and the volume (V) contained within the tire. The European Tire and Rim Technical Organization (ETRTO) expresses this relationship with the equation:
LCC=xcex1Vxcex2(P+P0)
where the xcex1 (alpha) and xcex2 (beta) coefficients are fixed by the ETRTO by interpreting the results of tire durability and endurance tests. Tire pressure (P) is the ETRTO basic inflation pressure. Similar calculations are employed in the United States by the Tire and Rim Association (TRA) to determine a xe2x80x9cLoad Indexxe2x80x9d (LI) comparable to the ETRTO""s load carrying capacity. A limitation on pneumatic tire sidewall changes is presented by the LCC (and LI). For example, if a shorter sidewall is desired (lower aspect ratio), then the tire width and/or outside diameter is usually increased to maintain approximately the same tire volume V at fill pressure P in order to maintain the same load carrying capacity LCC. Alternatively, the design of the tire can be changed in order to produce higher values for the LCC alpha and/or beta coefficients in ETRTO testing, thereby achieving the same LCC with a reduced tire volume V. Conventional radial ply tires with low aspect ratios have been developed in part to address the limitations of sidewalls. As noted by U.S. Pat. No. 4,811,771 (""771), there are basically two different shapes of passenger tires on the road today: high aspect ratio tires (aspect ratio  greater than 65) and low aspect ratio tires (aspect ratio  less than 65). The low aspect ratio tires, where the radial height of the sidewall is reduced relative to the tire width, have better cornering characteristics and less rolling resistance than the high aspect ratio tires. Patent ""771 discloses the use of a special low aspect ratio tire (aspect ratio of 40 to 45) used in conjunction with a new larger diameter wheel and rim (18 to 20 inches).
Recognition of the advantages of reducing the radial height of the sidewall is not new. U.S. Pat. No. 1,293,528 discloses the use of a plurality of chain rings as an xe2x80x9cinexpansiblexe2x80x9d bond to provide a pneumatic tire having a cross section under inflation to present a most advantageous width for weight carrying capacity and which will have only the minimum radial height necessary to provide the requisite cushioning action, so that the wheel rim may be as close as practicable to the surface traveled over and the driving power thereby most efficiently transmitted.
U.S. Pat. No. 1,456,062 (""062) discloses a tire that has no straight sidewalls or belly part, independent of its wide gable-like tread, as in existing types of inflated tires. In fact the whole of the tire cover, with the exception of its suitable inextensible base beads is a shock absorbing tread, which xe2x80x9cmay be used to replace existing types of solid rubber band tiresxe2x80x9d. The tread is arced, with a narrow blunt apex on its centerline, so that the footprint varies in size with the applied load. As best it can be determined from the description in this 1923 patent, the tire does not have belts or beads in the same sense as modern-day tires. The patent mentions xe2x80x9cinextensible base beadsxe2x80x9d but describes and illustrates these beads as being part of xe2x80x9can abnormally strong and preferably thin supple foundation . . . which may be manufactured from woven cord and be endless and abnormally strong in every direction. This unbelted, non-radial ply tire also provides rim flange protection and limited run flat capability as seen in FIG. 3 of the ""062 Patent, where the flattened, deflated tire is thick enough to support the vehicle by pressing against the substantially flat well of the wheel without loading the wheel rim flanges.
Other patents describe tires, such as racing tires, with aspect ratios as low as 25% but still having sidewalls. For example, German Patent No. 25 34 840 discloses a low aspect ratio tire with a running tread having a width which is at least half the total width of the tire, and preferably less than two-thirds of the total width of the tire. The remainder of the tire width comprises sidewalls which are radially diverted towards the seating surfaces of the tire rim.
German Patent No. 2 127 588 discloses a very low profile pneumatic tire for racing cars (aspect ratio less than 25%) having a broad tread molded in a concave shape so that it becomes flat when the tire is inflated at low pressure. The maximum width of the rim is 120% of the wheel diameter. The tire may be of radial or crossply construction. The outside surface of the sidewall is substantially flat and vertical in an un-inflated tire, however the ply line has a standard curvature from the bead into the sidewall.
U.S. Pat. No. 5,785,781 discloses a tire with relatively straight sidewalls combined with a tread-supporting ring on a specially-designed rim, in order to provide support for the tire when running at low or zero pressure. The tire has a radial ply casing on which the points that are furthest apart axially are radially apart close to seats of outwardly sloping beads, which engage sloping seats on the rim which also features an extra rim flange axially interior to the bead. When mounted on the specially-designed rim and inflated to service pressure, the tire""s carcass reinforcement (ply) has a constant direction of curvature from the bead area to the corresponding sidewall wherein a tangent to the point of tangency of the [ply line] with the [bead] reinforcement ring forms with the axis of rotation an angle xcfx86, open towards the outside, of at least 70xc2x0, preferably at least 80xc2x0, and even more preferably greater than 90xc2x0 as mentioned on column 5, lines 40-61. The base of each rim bead seat slopes at an angle formed with the axis of rotation wherein the angle is open axially inward and radially outward and is greater than 0xc2x0, preferably between 10xc2x0 and 40xc2x0. The axially outside rim flange delimits the bead tip with a face which forms with the axis of rotation an angle xcex3, open radially and axially towards the outside, of less than 90xc2x0 and preferably between 40xc2x0 and 50xc2x0.
While it may not be readily apparent, there exists a potential to develop a pneumatic radial tire with revolutionary dimension properties providing superior performance when compared to conventional pneumatic radial tires. The challenge is to develop such a tire combining improved handling and performance with adequate radial flexibility, sufficient rim flange protection and enhanced run flat capability suitable for use on conventionally-shaped (i.e., standard) wheel rim designs.
The present invention concerns changes to the ply line and bead area construction of pneumatic tires in order to achieve an increased load carrying capacity (extended load index) for pneumatic tires designed to mount on conventional, commercially available wheel rims.
According to the invention, a pneumatic tire with an increased load carrying capacity (extended load index) but compatible with conventional, commercially available wheel rims, has a modified carcass ply line. The tire has a tread area, a carcass structure including two bead areas each comprising a bead, at least one cord-reinforced elastomeric ply extends between the two bead areas, and two sidewalls extending between the tread area and each bead area. The tire has a section width (SW) defined by lines L1 and L2 disposed orthogonally to the axis of rotation AR and at a distance of A/2 from the equatorial plane EP of the tire, lines M1 and M2 each parallel to lines L1 and L2, respectively, and axially inwards toward the equatorial plane EP and spaced a distance d1, d2, respectively, of 1 mm to 4 mm from lines L1 and L2, points P1, P2 on lines M1 and M2, respectively, located at the minimum radial distance of dp1, dp2, respectively, from the at least one elastomeric ply to an axis of revolution AR of the tire, the elastomeric ply having a plyline PL including points P1 and P2, the plyline PL extending radially outward from points P1 and P2 a radial distance r1, r2, respectively, to the crown portion CP of the tire without axially deviating from lines M1, M2 by more than a distance d3, d4 of 0 mm to 6 mm. R1, r2 are defined as having a value that exceeds the distance dp1, dp2 by a value of 30% to 70% of the section height SH.
According to the invention, r1, r2 are defined as having a value that exceeds the distance dp1, dp2 by a value of 30% to 70% and preferably 40% to 60% of a section height SH of the tire. The ply line (PL,PLxe2x80x2) extends radially outward in the sidewalls from each bead at an angle xcfx86 to the axial direction (A) and the sidewall ply line angle xcfx86 opens radially outward and is in the range of 80 degrees to 100 degrees. Each bead area has a cross sectional shape which is substantially flat across a bead base having a rim bead seat line which forms an angle xcex1 to the axial direction (A) wherein the angle xcex1 opens axially and radially outward and is in the range of 5 to 20 degrees. Each bead area has a cross sectional shape which is substantially flat along a rim flange line forming an angle xcex3 to the radial direction (R), wherein the angle y opens axially and radially outward and is in the range of 0 to 10 degrees.
The ply extends with a generally continuous curvature through each sidewall to a tread shoulder so that the tire section width is immediately radially outward of a flange on a rim used for mounting the tire. The ply extends through the sidewall around the bead, passing radially inward of the bead, and having a turned up end located adjacent to the main portion of the at least one ply radially outward of the beads and the bead area and the sidewall area radially outward of the bead and between the ply and the interior carcass wall is at least partially filled with an elastomeric reinforcement. The turned up end of the ply is axially outward of the main portion of the ply.
Also according to the invention, the turned up end of the ply is axially inward of the main portion of the at least one ply, and lies between the interior reinforcement and the main portion of the ply.
According to the invention, the elastomeric reinforcement is made of elastomeric material to reinforce the sidewalls of an extended mobility tire during extended mobility running while uninflated.
According to the invention, the ply can extend from each sidewall radially inward Ace around the bead, first passing axially outward of the bead, then passing radially inward of the bead, then passing axially inward of the bead, and finally extending radially outward to a reversed ply turnup end located axially inward of the main portion of the at least one ply and radially outward of the bead. The elastomeric reinforcement of this embodiment is between the main portion of the at least one ply and the reversed turnup portion of the at least one ply which ends at the reversed ply turnup end. This clastomeric material can be designed to reinforce the sidewalls of an extended mobility tire during extended mobility running while uninflated.
According to the invention, the pneumatic tire has a tread area, two bead areas, two sidewalls extending between the tread area and each bead area; and a carcass structure comprising an interior wall and at least one cord-reinforced elastomeric ply extending between the two bead areas. The ply has a sidewall ply line that extends radially outward from each bead at an angle xcfx86 to the axial direction. The sidewall ply line angle xcfx86 opens radially outward and is in the range of 80 to 100 degrees. In order to be compatible with conventional rims, each bead area has a cross sectional shape that is substantially flat across a bead base having a rim bead seat line which forms an angle a to the axial direction. The angle a opens axially and radially outward and is in the range of 5 to 20 degrees, and each bead area has a cross sectional shape which can be substantially flat along a rim flange line forming an angle xcex3 to the radial direction, wherein the angle xcex3 opens axially and radially outward and is in the range of 0 to 10 degrees.
In further aspects of the invention, the inventive ply line is achieved in various embodiments utilizing both outside and inside (reversed) ply turnup ends, and various forms of bead area reinforcing elements.
In a further aspect of the invention, the at least one ply extends from the sidewall around the bead, passing radially inward of the bead, and having a turned up end located adjacent to the main portion of the at least one ply radially outward of the beads; and the bead area, and at least a portion of the sidewall area radially outward of the bead and between the at least one ply and the interior carcass wall is at least partially filled with an elastomeric reinforcing interior bead reinforcing.
In alternate embodiments, the turned up end can be either axially outward or axially inward of the main portion of the at least one ply. For the inward (reversed) turnup end embodiments, the interior apex may be between the interior wall and the reversed turnup end, or the apex may be a center apex lying between the main portion of the at least one ply and the reversed turnup portion of the at least one ply which ends at the reversed ply turnup end. The apex elements are preferably shaped to produce a uniformly curved interior surface.
In a further aspect of the invention, the bead reinforcing elements are made of elastomeric material designed to reinforce the sidewalls of an extended mobility tire during extended mobility running while uninflated (running xe2x80x9cflatxe2x80x9d).
A feature of the invention is that the inventive tire can replace an existing tire on a wheel rim of conventional rim shape, but larger rim width and diameter, while maintaining the same load carrying capacity, outside tire diameter and section width as the existing tire.
An alternative feature of the invention is that the inventive tire can replace an existing tire with a smaller tire which still mounts on a wheel rim of conventional rim shape, but larger rim width, while maintaining the same load carrying capacity as the existing tire.
Other aspects, features and advantages of the invention will become apparent in light of the following description thereof.